Hajja, 19, escapes from Boko Haram den

In the gloom of a hilltop cave in Nigeria where she was held captive, Hajja had a knife pressed to her throat by a man who gave her a choice – convert to Islam or die.

Reuters reports that two gunmen from Boko Haram had seized the Christian teenager in July in the Gwoza hills, in the northeastern Nigeria, where a six-month-old government offensive is struggling to contain an insurgency by the al Qaeda-linked Islamist group.

Boko Haram is abducting Christian women whom it converts to Islam on pain of death and then forces into “marriage” with fighters.

The three months Hajja spent as the slave of a 14-strong guerrilla unit, cooking and cleaning for them before she escaped, give a rare glimpse into how the Islamists have changed tack.

“I can’t sleep when I think of being there,” the 19-year-old told Reuters, recounting forced mountain marches and watching her captors slit the throats of prisoners Hajja had helped lure into a trap.

Nigerian security officials say the Islamists have pulled back after army assaults since May on their bases and are now sheltering in the Mandara mountains. From the hills they have been launching increasingly deadly attacks.

Hajja’s account of how Boko Haram has adapted and survived in recent months underlines the difficulties governments in the region face.

The military offensive launched in mid-May, and the fact that large numbers of civilian vigilantes have supported it, has triggered a fierce backlash against local people by Boko Haram.

The Islamists dragged Hajja along rocky mountain paths and slept in caves in the hills, a landscape unfamiliar to most Nigerian soldiers, recruited from the plains.

She ceremonially converted to Islam, cooked for the men, carried ammunition during an attack on a police outpost and was about to be married to one of the insurgents before she managed to engineer a dramatic escape. She says she was not raped.

“They told me I must become a Muslim but I refused again and again,” Hajja told Reuters. Her family name is withheld to protect relatives still living in the Gwoza area.

“They were about to slaughter me and one of them begged me not to resist and just before I had my throat slit I relented. They put a veil on me and made me read from the Koran,” she said.

A man called Ibrahim Tada Nglayike led the group Hajja was with. On one mission, Hajja was sent to stand in a field near a village to attract the attention of civilians working with the army. When five men approached her, they were ambushed.

“They took them back to a cave and tied them up. They cut their throats, one at a time,” Hajja said.

Among those who did the killing was the Muslim wife of the leader Nglayike, the only other woman in the band of fighters.

Reuters verified Hajja’s account of having been abducted with independent figures in the region. Boko Haram shuns the media and could not be contacted for comment.

Hajja says the long-bearded insurgents lived a basic lifestyle, eating corn, millet and occasionally meat from animals.

The group, armed with AK-47 rifles and pistols stolen from police they killed, moved every day around the hills to avoid being tracked by the army and slept in the caves to shelter from the cold and for protection against air assaults.

“They didn’t use phones but they had a radio,” Hajja said.

“They would listen to BBC Hausa or Voice of America.

“They know the area very well and many people help them because they are afraid or support their cause,” Hajja said.

The longer the insurgency goes on, President Goodluck Jonathan, a southern Christian, will come under increasing criticism from his northern opponents as elections in early 2015 draw closer.

Hajja eventually escaped by feigning severe stomach pains. Thinking her too ill to flee, the insurgents sent her to hospital escorted only by an older woman. Once she was among other people, Hajja threatened to denounce the group to police, prompting the woman to abandon her and flee.

“I finally tore off the veil and I cried,” Hajja said.

“So many times I thought I’d die.”